1. Field of the Invention:
The present invention relates to a method of and an apparatus for cleaning a workpiece, and more particularly to a method of and an apparatus for cleaning a substrate such as a semiconductor substrate, a glass substrate, or a liquid crystal panel to a high level of cleanliness.
2. Description of the Prior Art:
As semiconductor devices become more highly integrated in recent years, circuit interconnections become thinner and the distances between those interconnections also become smaller. While processing a semiconductor substrate, particles such as minute semiconductor particles, dust particles, or small crystalline pieces tend to be attached to the semiconductor substrate. If particles existing on the semiconductor substrate are greater in size than the distances between interconnections on the semiconductor substrate, then short-circuits will possibly be developed between the interconnections. To avoid such a drawback, any particles present on the semiconductor substrate are required to be sufficiently smaller than the distances between interconnections on the semiconductor substrate. This holds true for the processing of other substrates including a glass substrate for use as a photomask, a liquid crystal panel, etc. To meet such a requirement, there has been demands for a cleaning process capable of removing smaller particles in the submicron level from semiconductor substrates and other substrates.
It has heretofore been customary to clean a semiconductor substrate by scrubbing it with a cleaning member made of a brush or a sponge.
Research efforts have been made to find a cleaning member which can exhibit a cleaning effect better than the brush or the sponge. As a result, it has been found that an abrasive cloth, used in recent years to polish the surface of a semiconductor wafer to planarize the same in its fabrication process, is effective to clean a workpiece, as proposed in Japanese patent application No. 7-129588 (corresponding to U.S. patent application Ser. No. 08/434,754, now abandoned).
In scrubbing a workpiece with a cleaning member such as a brush, a sponge, or an abrasive cloth, since the cleaning member is held in direct contact with the workpiece, the cleaning effect of the cleaning member depends on the contamination of the cleaning member. Specifically, as the contamination of the cleaning member which is contaminated by the contaminant removed from the workpiece progresses, the contaminant deposited on the cleaning member contaminates the workpiece again, thus lowering the cleaning effect which the cleaning member has. Such a phenomenon is referred to as a reverse contamination. The cleaning member has to be replaced with a fresh cleaning member before the cleaning member causes the reverse contamination.
Replacing the cleaning member with a fresh cleaning member requires the cleaning apparatus to be shut off. Consequently, the processing capability of the cleaning apparatus is lowered, and dust particles produced in a cleaning environment by the replacement of the cleaning member poses problems.
It is desirable to purify the cleaning member without replacing the same when it is contaminated. Such a purifying process is known as a self-cleaning process. According to the conventional self-cleaning processes, it has heretofore been customary to rinse the cleaning member in a cleaning liquid or apply a water jet or an ultrasonically vibrated water stream to the cleaning member.
Inasmuch as the self-cleaning of the cleaning member governs the cleaning effect thereof, prolongs a service life of the cleaning member, and increases the processing capability of the cleaning apparatus, there have been demands for more effective self-cleaning processes.